This Core will be responsible for the generation and characterization of the ambient aerosols to conduct inhalation exposures. The ambient particle concentrator system that we have recently developed will be used to generate ambient aerosols at desirable levels, under controlled temperature and relative humidity conditions. Using a number of continuous and time-integrated samplers the physical chemical, and biological properties of the particles supplied to the inhalation chamber will be determined. Particle mass concentration, size distribution, inorganic ions and strong acidity, trace metals, elemental carbon, as well fungal and pollen spores and endotoxin concentrations will be determined. In addition, the oxidation generating potential of particles will be measured. Furthermore, particle samples will be collected for subsequent in vitro cellular studies. Finally, gaseous air pollutant concentrations, including carbon monoxide, ammonia, nitrogen dioxide, and nitric oxide will be monitored. Depending on optional experimental conditions, ozone, nitric and nitrous acids, and sulfur dioxide concentrations will also be measured, when a diffusion denuder system is not placed upstream of the exposure chamber to remove these gases. This Core relates to the other Projects because it proviede generation and characterization of ambient aerosols for both in vivo and in vitro studies. In addition, since the core includes experts in atmopheric sciences and biostatistics, it will provide support to all projects in understanding the sources and types of particles and in relating the observed biological effects to the various measured particle attributes. Therefore, the intent of this core is not only to provide the engineering expertise and facilities for generating and characterizing the exposure atmospheres but also to integrate the exposure and health effects studies in this project. This will be of paramount importance for both the interpretation and synthesis of the collected data.